percpu: move generic {raw|this}_cpu_*_N() definitions to include/asm-generic/percpu.h

{raw|this}_cpu_*_N() operations are expected to be provided by archs
and the generic definitions are provided as fallbacks.  As such, these
firmly belong to include/asm-generic/percpu.h.

Move the generic definitions to include/asm-generic/percpu.h.  The
code is moved mostly verbatim; however, raw_cpu_*_N() are placed above
this_cpu_*_N() which is more conventional as the raw operations may be
used to defined other variants.

This is pure reorganization.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>